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United States Department of Transportation United States Department of Transportation

Public Roads - Autumn 2021

Date:
Autumn 2021
Issue No:
Vol. 85 No. 3
Publication Number:
FHWA-HRT-22-001
Table of Contents

Bolstering the Safety of America’s Bridges for Half a Century

by Joey Hartmann

It is in the vital interest of the United States to have a strong national bridge inspection program and maintain an inventory of the Nation’s bridges. Regular and thorough bridge inspections are necessary to maintain safe operations and prevent structural and functional failures. In addition, data on the condition and performance of bridges are necessary for bridge owners to make informed investment decisions as part of an asset management program.

Safety—including bridge safety—is the Federal Highway Administration’s top priority. The agency’s longstanding and successful national bridge inspection program has been at the core of highway bridge safety, and 2021 commemorates its 50th anniversary. The program requires regular bridge inspections and data collection by trained professionals.

FHWA adopted the National Bridge Inspection Standards (NBIS) regulations in 1971, prompted by the U.S. Congress enacting the Federal-Aid Highway Act of 1968. The NBIS were the direct result of the Silver Bridge collapse in Point Pleasant, WV, on December 15, 1967. The tragic event brought nationwide attention to the issue of bridge safety and led to a systematic effort to ensure bridge safety at the national level—and the birth of FHWA’s Federal program. It was an event of historical significance and one that many would agree was a wake-up call that propelled the Nation into a new era of bridge safety.

"An inspection using a bucket truck on a bridge on Foothills Parkway. Image Source: FHWA."
The Federal Highway Administration adopted the National Bridge Inspection Standards (NBIS) in 1971. Bridges, like this one on Foothills Parkway in Tennessee, are inspected following the program’s standards.

By 1971, when the NBIS were established, the new standards required that bridges, and their various component parts—ranging from pilings to deck slab—be inspected at least once every 2 years, with special emphasis on identifying and assessing fractures, corrosion, and fatigue. In addition, FHWA was ultimately charged with using the data from bridge inspections nationwide to create the National Bridge Inventory (NBI) and to standardize bridge inspector qualifications.

“The Silver Bridge tragedy and the resulting legislation drastically changed the way we approached bridge safety and made sure that the hundreds of millions of Americans who have driven over a bridge any time in the last 50 years were safer in doing so,” says Thomas D. Everett, FHWA’s Executive Director.

In addition, the tragedy raised many questions about the state of bridges nationally. For starters—How many bridges were there in the United States? How were they designed, what were they made of, and how old were they? How much traffic did they carry? There were no answers to basic questions like these, because there was not yet a nationwide collection of bridge information. The establishment of the NBIS aimed to answer these questions.

A half century later, FHWA’s bridge inspection standards continue to ensure that only bridges safe for travel are open to traffic.

Timeline of Bridge Program Evolution 

Over the last decade, FHWA has implemented new measures to boost its oversight role and to target the inspection of areas critical to bridge safety. For example:

  • In 2011, FHWA instituted a risk-based, data-driven approach to more clearly and easily identify bridge inspection issues in each State. FHWA replaced written general assessments of State bridge inspection programs with measurements of 23 key metrics to more easily identify potential safety issues. The newer process provides for more bridge inspection consistency and simplifies efforts to identify challenges State by State.
  • In 2015, FHWA began collecting new data for bridges on the National Highway System to more closely monitor bridge conditions nationwide. Previously, bridge inspectors assigned one summary rating for the condition of a bridge’s major components to reflect both the severity of a problem and whether it was widespread or confined to a small area. The new format calls for each square foot of the bridge deck to be assigned a rating, and its other elements—such as the joint seals—receive separate ratings. Dividing bridge components into smaller, more manageable elements helps engineers more easily assess the extent of bridge deterioration, which leads to more informed decisions about preservation, repair, and replacement.
  • FHWA is in the process of updating the NBIS. A Notice of Proposed Rulemaking was published on November 12, 2019, and the comment period was open until March 13, 2020. FHWA has been reviewing the comments received and is preparing a Final Rule.

A Robust Program 

FHWA provides oversight of State bridge inspection programs. While States, local agencies, Federal agencies such as the National Park Service, and Tribal governments own most highway bridges, FHWA maintains the NBIS—the Federal bridge inspection regulations that States, Federal agencies, and Tribal governments are required to follow. The NBIS apply to all highway bridges on all public roads. FHWA assesses compliance with the regulations through a detailed annual review process.

Working with FHWA division offices, State transportation departments, and Federal agencies, hundreds of qualified inspectors from the NBIS program evaluate the condition and safety of the Nation’s highway bridges every day. These bridges are inspected on a routine basis, typically every 24 months, and the results are reported to FHWA. If inspectors deem a bridge unsafe, immediate action is taken, which may include closure, prompt repair, or load posting (weight limit) that does not allow heavy vehicles to use the bridge.

"Inspectors assess the concrete of a bridge. Image Source: FHWA."
An inspection of the John Coffee Memorial Bridge, part of the Natchez Trace Parkway over the Tennessee River.

FHWA continues to maintain the comprehensive NBI, a compilation of bridge data that States and Federal agencies provide to FHWA on an annual basis. It contains more than 100 data items for each of the Nation’s approximately 618,000 highway bridges, representing a database of more than 60 million pieces of information.

“FHWA’s NBI has gotten more robust over the years. Just looking at the data amassed in the 21st century, the number of highway bridges has grown from 587,735 in 2000 to 618,456 today,” says Hari Kalla, the Associate Administrator for the FHWA Office of Infrastructure. “Bridge owners continue to build new bridges and replace or rehabilitate others that have deteriorated. Today, the average age of the 618,000 highway bridges in the NBI is 45 years old. The oldest bridge in the NBI is in Pennsylvania and was built in 1697. In fact, there are more than 1,700 bridges built before 1900 that are still being used today.”

The program has been successful in identifying bridge deficiencies, while Federal and other funding programs have supported efforts to address these deficiencies. As owners have repaired bridges, the percentage of bridges in poor condition has dropped from 11.9 percent in 2000 to 7.3 percent in 2020. Bridge conditions have steadily improved over the years due to the commitment to bridge safety by FHWA and State departments of transportation.

While State departments of transportation are on the front lines conducting the inspections, FHWA provides the standards and oversees State programs to ensure safety and track bridge conditions nationwide. FHWA has worked constantly over the years to improve the national program and ensure that bridge inspections continue to be robust.

The agency is continually committed to finding new and better ways of making sure bridges are safe.

Flexible Response to Bridge Safety Challenges 

Since FHWA established NBIS regulations in 1971, the agency has worked to evolve, improve, and refine the program on an ongoing basis. Some improvements have included requiring more rigorous inspections for certain steel bridges with less redundancy, requiring underwater inspections for bridges over water, and taking appropriate and timely followup actions when inspections identify critical safety issues. FHWA has also updated training requirements for bridge inspectors.

Another bridge tragedy occurred on August 1, 2007, when the Minneapolis I–35W Bridge collapsed during evening rush hour. Although the collapse was not a result of a failed inspection, it brought renewed interest in the bridge inspection program.

"The Minneapolis I–35W Bridge after its collapse into the Mississippi River and the surrounding land. Image Source: FHWA."
The Minneapolis I–35W Bridge collapse in August 2007, while not a result of failed bridge inspections, sparked renewed interest in the NBIS program.

In response, FHWA moved from a qualitative process to a risk-based, data-driven process in 2011 to assess compliance with the NBIS. FHWA now requires annual assessments using a grid of 23 specific inspection program areas to determine how well State transportation departments and Federal agencies are meeting the regulations. In addition, FHWA dedicated more staff to support bridge inspection efforts. The aim was to improve consistency in bridge inspections and simplify efforts to identify challenges State by State. FHWA also expanded the amount of data collected on bridges to more closely monitor bridge conditions nationwide.

Key Bridge Rating Definitions 

  • Good – A bridge classified in good condition has all primary bridge components rated in good condition or better. Good condition would indicate the structural elements of the bridge have no deterioration or some minor deterioration. A bridge in good condition may need preservation or cyclic maintenance activities.
  • Fair – A bridge classified in fair condition has one or more primary bridge components rated in satisfactory or fair condition, and none of these components rated worse than fair condition. Fair condition would indicate that some structural elements of the bridge have minor deterioration that could include section loss, cracking, spalling, scour, or other defects of similar significance. Typical needs of a bridge in fair condition would include preservation, cyclic maintenance activities, or condition-based maintenance activities.
  • Poor – A bridge classified in poor condition has one or more primary bridge components rated in poor or worse condition. Poor condition would indicate that some structural elements of the bridge have advanced deterioration. Typical needs of a bridge in poor condition would include condition-based maintenance activities, rehabilitation, or replacement. A bridge in poor condition may require more frequent inspections, closer monitoring, or weight restrictions to ensure it remains safe for public travel. Unsafe bridges are closed.

Tradition Alongside Technology 

FHWA continues to explore new ways of keeping bridges safe, including using unmanned aerial vehicles, also known as drones, and various other cutting-edge tools to support or assist bridge inspections. Applying science and technology to such matters helps inspect bridges more quickly, and more thoroughly, than ever before. On any given day, hundreds of bridges are being inspected across the country and evaluated by qualified inspectors.

"Inspectors perform ultrasonic testing, a nondestructive evaluation technique, on a bridge. Image Source: FHWA."
Inspectors perform ultrasonic testing, a nondestructive evaluation technique, on two bridges.
"Inspectors perform ultrasonic testing, a nondestructive evaluation technique, on a bridge. Image Source: FHWA."
Inspectors perform ultrasonic testing, a nondestructive evaluation technique, on two bridges.

Despite certain advances in technology, however, physical and visual inspection methods continue to be valuable in the inspection world. These remain the primary tools in the toolbox that bridge inspectors use in assessing the condition of a bridge. Other technology-based tools used by bridge inspectors are sometimes referred to as advanced inspection methods, or nondestructive evaluation (NDE) techniques. These include methods such as ultrasonic testing, which uses sound much like a sonogram to detect subsurface characteristics, and infrared thermography, which uses the heat radiating from bridge components as an indicator of their condition.

“In addition to traditional, manual methods, the bridge inspection industry has embraced technological advances when they can add value to the inspection results,” says Cheryl Richter, Director of the FHWA Office of Infrastructure Research and Development.

FHWA supports the use of advanced technology, including the use of drones, to supplement bridge inspections. Technologies may not replace the human inspector at this time, but they can accelerate inspections and improve inspector safety. NDE technologies can be used to improve the accuracy of some inspections and the proper identification of certain issues. Bridge inspectors are trained to identify when those technologies are needed.

Bridge Inspection Technologies

  • Acoustic emissions testing
  • Acoustic wave sonic/ultrasonic testing
  • Dye penetrant testing
  • Magnetic particle testing
  • Magnetic flux leakage testing
  • Eddy current testing
  • Ground-penetrating radar
  • Stress wave/pulse velocity testing
  • Impact echo testing
  • Infrared thermography
  • Magnetic field disturbance testing
  • Radiographic and other nuclear methods
  • Vibration testing

Looking Toward the Future 

FHWA is in the process of updating the NBIS to address statutory requirements, provide flexibility, and address ambiguities identified since the last update to the regulation in 2009. The improvements will include expanding the requirements to Tribally owned highway bridges, updating the training and qualifications for bridge inspectors, and establishing a national certification for inspectors. In addition, requirements for the intervals between inspections will be updated using a risk-based approach, and procedures for the reporting and monitoring of critical findings will be established. The changes are primarily aimed at ensuring the uniformity of inspections and evaluations and clarifying responsibilities.

Joseph (Joey) Hartmann, Ph.D., P.E., is the director of FHWA’s Office of Bridges and Structures.

For more information, contact Joey Hartmann at joey.hartmann@dot.gov or visit www.fhwa.dot.gov/bridge.

"Inspectors use a bucket truck to inspect the Snake River Bridge. Image Source: FHWA."
Inspectors use a bucket truck on the Snake River Bridge in Grand Teton National Park.